Most indicators for the quarter that ended Sept. 30 suggest PC sales are on the upswing. Two research companies, IDC and Gartner, reported double-digit worldwide sales growth year-over-year  15.7 percent from IDC and 14.1 from Gartner. In the United States, the figures were 16.1 and 19.1 percent.

That equates to 38 million to 42 million computers sold globally during the period, depending on which figures are cited.

The numbers are encouraging to a sector that has been languishing for the past three years, battered by the dot-bomb, a flagging economy and a mountainous inventory of used equipment that sold at auction for far less than even the cheapest new computers.

As moribund as 2003 looked a few months ago, PC sales were not supposed to show even a hint of rebound till the fourth quarter, when holiday shopping traditionally provides a boost. Analysts still are offering a cautious outlook, saying early 2004 may witness another dip.

While I doubt we'll see a return to the glory years of 20 percent growth quarter after quarter, I also believe the worst is over for PC sales. The reason: Equipment purchased before 2000 before the Y2K crisis (which never happened) is getting old. The same holds true for the dot-com inventory.

Those millions of computers will have to be replaced over the next year or two.

Upgrades beget more upgrades. People talk about their new machines. And they do more with the upgraded equipment, boosting software and Web applications. In three areas, expanded capabilities are driving PC upgrades:

One is high-speed Internet access. Content is booming: There's a lot of video, its resolution is improving and music services continue to thrive. Broadband is getting cheaper, and more people are logging on: In September more than 150 million Americans used the Internet, the most ever, says comScore Media Metrix.

Another is CD and DVD burning. Digital cameras and camcorders, along with improved PC software, are creating a boom in content-sharing. Blank CDs have surpassed recorded CDs in sales, and digital photos have overtaken film.

Finally, there's portability. Wireless Internet access through home and public Wi-Fi networks is pushing laptop and notebook sales to record levels. Especially for kids, the portable PC is becoming requisite.

Another big factor looms: Microsoft's release of the next version of Windows, code-named Longhorn. It's an ambitious project and may not be publicly available till 2006 or 2007. But it will almost certainly drive equipment upgrades on several fronts.

It's probably a bit early to expect a minimum-requirements list for Longhorn. We can hope that Microsoft, as soon as is practical, will settle on a "base machine" for the upgrade. That will give guidance on memory and processor requirements to those forced to replace aging equipment before Longhorn's release.

When I refer to PC sales and upgrades, I include Apple Macintoshes and Linux PCs in the mix. Apple is doing some remarkable innovation in the digital-lifestyle category, and Linux continues to get better, to the point it already provides a workable alternative to Windows in many categories.

In any case, the PC is back. Even though doubts about economic recovery continue, rising PC sales can't help but drive the tech sector back to health  starting with the upcoming holiday season.